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Anne-Sarah Caldara, Eugene Mayer, Roberto Caldara; The occipital face area is not necessary for symmetry perception in faces. Journal of Vision 2008;8(6):402. doi: 10.1167/8.6.402.
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Symmetry pervades our visual world. Many biological organisms have acquired a particular sensitivity to subtle symmetry detection cues in their environment and conspecifics. The balanced distribution of duplicate body parts is a fundamental characteristic of living organisms, and for many biological species this structural property seems to be related to their phenotypic condition - an aspect that plays a key role in mate selection. Symmetrical human faces are perceived as sexually attractive, healthier and more intelligent - all representing crucial factors for social and biological interactions. Interestingly, symmetry detection is better for upright compared to inverted faces despite these visual stimuli are matched for their low-level properties (Rhodes, et al. 2005), suggesting that high-order mechanisms subtend to this human ability. Recently, the neural bases of facial symmetry perception have been investigated within the face-sensitive regions using functional Magnetic Resonance Imaging (fMRI). Chen et al. (2006) found sensitivity for symmetry uniquely in the right Occipital Face Area (rOFA), whereas Caldara and Seghier (2006) found such sensitivity only in the right Fusiform Face Area (rFFA). Consequently, the identification of the neural substrates involved in the processing of facial symmetry remains to be clarified. Here we tackled this discrepancy by testing facial symmetry perception in PS, a pure case of prosopagnosia, with a lesion encompassing the rOFA and sparing the rFFA (Sorger et al., 2007). We confronted PS and an age-matched control group of participants with a normal and a perfectly symmetrical version of the same face. The face-pairs were presented for 200ms and 500ms in separate blocs. PS identified symmetrical faces as accurately as the controls, showing that prosopagnosia does not necessarily involve a deficit in symmetry perception. Crucially, these observations provide unequivocal evidence that symmetry perception for faces does not rely on neural populations within the rOFA.
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